A rotating electrical machine that is mounted on a hybrid electric vehicle, an electric vehicle, and the like includes a rotor and a stator that is arranged at an outer diameter side of the rotor on which a stator coil is wound.
For giving driving force to the vehicle by the rotating electrical machine, electrical current is passed through the stator coil so as to give rotational force to the rotor. In addition, when generating electric power by the rotating electrical machine, current generated at the stator coil by rotation of the rotor is obtained.
At this time, heat is generated at the stator coil and the stator core due to loss in the rotating electrical machine. Insulation material used for the rotating electrical machine has an upper temperature limit to assure insulation performance, and the rotating electrical machine needs to be cooled so as not to exceed the temperature limit.
There are two types of cooling methods to cool rotating electrical machines, i.e., an air cooling method in which air is used as a cooling medium and a liquid cooling method in which liquid is used as a cooling medium. There are two types of liquid cooling methods, i.e., an indirect cooling method in which cooling liquid is caused to flow through a liquid cooling jacket provided at an outer diameter side of the stator core and the like so as to perform cooling through the liquid cooling jacket and a direct cooling method in which an insulating liquid such as oil is directly applied to a heat generating region of the rotating electrical machine such as the stator coil so as to cool the region.
The direct cooling method allows the overall size of the rotating electrical machine to be reduced because no liquid cooling jacket is needed and also has an excellent cooling performance because a cooling medium can be directly applied to a heat generating region, so that the direct cooling method is adopted in a multitude of rotating electrical machines.
Patent Literature 1, for example, discloses a cooling system in which a cooling medium passage is provided on an outer circumference side of a stator and a cooling medium is spouted from an outlet port bored in the cooling medium passage to a stator coil end, so that a coil is cooled by the cooling medium flowing on the surface of the stator coil end due to jet pressure and gravity.